1. Field of the Invention
The present invention concerns a method for monitoring the power state (power status) of an x-ray radiator and/or an x-ray detector. The invention additionally concerns a system to implement such a method.
2. Description of the Prior Art
An x-ray radiator and an x-ray detector are normally components of an x-ray device. The x-ray radiator serves to generate and to radiate x-rays, the x-ray detector to detect x-rays. X-ray devices today have found usefulness in the most varied technical fields, which has resulted in the dissemination of x-ray radiators and x-ray detectors in these fields. For example, material sciences, safety engineering and medical engineering are among these technical fields in which x-ray radiators and x-ray detectors are used.
In particular in medical engineering it is desirable to keep the x-ray exposure of a subject to be examined as low as possible. For this purpose, it is necessary that the x-ray radiator and x-ray detector have a power state situated within certain specification limits in order to ensure a sufficient image quality. For example, the power state of the x-ray radiator encompasses properties of the x-rays that can be radiated by the x-ray radiator, in particular the intensity of the x-rays as well as their spatial (advantageously homogenous) distribution over an x-ray beam diameter. The power state of an x-ray detector normally involves properties of the x-ray detector that have an effect on the image quality in the detection of x-rays.
A failure of the x-ray radiator and/or x-ray detector or a significant reduction of the image quality that can be achieved by means of the x-ray radiator and x-ray detector is undesirable during clinical operation, in particular while conducting an x-ray examination of a patient. A particular disadvantage is that a repetition of the radiation exposure for the subject to be examined may be required by the physician to enable the diagnosis given a failure of the x-ray radiator and/or of the x-ray detector during the examination of the subject. This has the result of an increase radiation exposure for the subject to be examined.
The image quality is significantly influenced by the intensity of the x-rays striking the x-ray detector, the subject to be irradiated, and the properties of the x-ray radiator and x-ray detector. For example, the noise response of the x-ray detector, the signal-to-noise ratio and the quantum efficiency of the x-ray detector are significant parameters characterizing the power state—for example image quality or sensitivity—of the x-ray detector.
These properties of the x-ray detector and/or x-ray radiator that are essential to the image quality can change over time, in particular to the detriment of the image quality. If these properties of the x-ray radiator and/or x-ray detector change significantly in the course of time, such that the image quality of x-ray exposures produced with them no longer appears to be sufficient to achieve an examination goal, an exchange of the x-ray radiator and/or of the x-ray detector is necessary. This leads to an increased downtime of the x-ray detector, as well as to an increased radiation exposure of the patient since a new radioscopy of the patient with x-rays is required.
The causes for the degradation of the image quality can lie both in an x-ray detector and in an x-ray radiator. In an x-ray detector that directly converts the x-rays into an electrical signal (using amorphous selenium to detect x-rays, for example), a degradation of the image quality can be caused by localized re-crystallization of the amorphous selenium within the x-ray detector matrix detecting the x-rays, for example.
A degradation of the image quality (for example due to high operating temperatures of the scintillation crystal) can also occur in indirectly converting x-ray detectors, which normally operate with a scintillation crystal (possibly a thallium-doped sodium iodide crystal or a sodium-doped cesium iodide crystal).
An aging which leads to a degradation of the image quality can likewise occur in an x-ray radiator. In particular, the aging can affect the anode of the x-ray radiator as well as the focal ring thereof, by the focal ring becoming roughened and melted at points by the tube current in the generation of the x-rays. This leads to a decrease of the x-ray radiation power with time given otherwise constant operating conditions or operating parameters of the x-ray radiator (for instance tube voltage and tube current).